A process for the preparation of multi-nuclear aromatic polyamines by the condensation of aromatic amines with formaldehyde in the presence of water and acid catalysts is described in U.S. application Ser. No. 383,921, filed July 30, 1973 and now U.S. Pat. No. 3,996,283. In that process, the aqueous condensation mixture obtained after the reaction has been completed is extracted with a hydrophobic solvent without neutralization of the catalyst. The desired polyamine is then isolated from the solvent phase while the aqueous phase, which contains the acid catalyst in the form of amine salts, is returned to the beginning of the process with the addition of fresh amine.
The above mentioned process marked a major improvement compared with the previously known processes for aniline/formaldehyde condensation using acid catalysts, particularly since it obviated the need for neutralization of the acid catalyst. As a result, the effluent water from the process is substantially salt-free. Additionally, there is practically no consumption of acid catalyst or of alkalizing agent.